Unhappy as a boy, Kim became youngest ever transsexual at 12

A boy of 12 is believed to have become the world's youngest sex change patient after convincing doctors that he wanted to live the rest of his life as a female.

The boy - originally called Tim, but now known as Kim - has started to receive hormone treatment, in preparation for the operation that will eventually complete the sex change.

Tim was diagnosed as a transsexual two years ago, when doctors and psychiatrists concluded that his claims to be "in the wrong body" were so deeply felt that he required treatment. The therapy involves artificially arresting male puberty, with a series of potent hormone injections before the administration of female hormones to initiate the development of features such as breasts.

Now aged 14, and officially registered as a female, Kim looks like a typical girl of her age. She dresses in fashionable clothes, has long blonde hair and blue eyes and dreams of moving to Paris to become a fashion designer. Her parents, who initially assumed their son was going through a temporary phase, eventually grew accustomed to seeing him as a girl.

The family's full identity has not been made public. But Kim's father, known as Lutz P. – speaking to the German publications Der Spiegel and Stern – said that as a child, the boy liked to play with Barbie dolls, enjoyed wearing dresses and, from the age of two, insisted that he was a girl. "We saw Kim as a girl, but not as a problem. Our life was surprisingly normal."

Kim reacted badly to the first signs of puberty, he said. "At that stage we realised that she was terrified of growing facial hair and her voice breaking."

Kim's parents consulted psychiatrists across Germany. Some condemned their support of their child's desire to undergo a sex change, or suggested that Kim be kept under observation in a closed psychiatric ward. But others agreed that the child should receive therapy, because growing up to be a man would have damaged her personality.

Dr Bern Meyenburg, the head of a clinic for children and adolescents with identity disturbances at Frankfurt University, concluded that the child was serious. He wrote in his diagnosis: "Kim is a mentally well-developed child who appears happy and balanced. There is no doubt of the determined wish, that was already detectable since early childhood. It would have been very wrong to let Kim grow up to be a man. It is rare to have such a clear-cut case."

Kim is reportedly fully accepted by her fellow school pupils and teachers. The costs of the procedure are being covered by health insurance, as the condition qualifies as an illness.

Dr Achim Wuesthof, an endocrinologist specialising in children and adolescents, who is treating the teenager at a clinic in Hamburg, said the procedure had been a success so far. Speaking to The Sunday Telegraph, he said that even though under-16s were not permitted to undergo a sex change in other countries, he and his colleagues felt that in this case it had been best to start earlier. He said: "To the best of my knowledge, Kim is the youngest sex change patient in the world. According to German law, two independent psychiatrists must confirm that the child is indeed transsexual and approve the sex change. Once that has been done, it is best to start as early as possible.

"Transsexuals experience the onset of puberty, and the physical changes it brings, as a serious trauma. But there is a general lack of empathy with cases like Kim's, mostly because people know little about the condition. Imagine a man that suddenly starts growing breasts or a woman that starts growing a beard against their will – that is how Kim and people like her experience puberty.

"They are not freaks, nor do they suffer mental illness. They are simply trapped in the wrong bodies. That is why it is best to help them as early as possible and reduce the trauma for them and their families."

The problem that Dr Meyenburg and other psychiatrists faced was distinguishing a true transsexual personality from a temporary gender identity crisis. Dr Meyenburg quoted an example of a 15-year-old girl who wanted to change her sex, but who revealed during counselling that she had suffered brutal sexual abuse by her father – a case for psychological, rather than hormonal therapy.

Should Kim change her mind before the surgery, the procedure could be reversed. Doctors admit that the treatment involves a risk, however, and that its effects on children as young as Kim are not fully understood.

For legal reasons, the final stage – cosmetic surgery to remove the male genitalia – cannot take place until Kim is 18. Britain's youngest transsexual is Angel Paris-Jordan, who was granted an operation on the NHS at the age of 17.